1. Field of the Invention
The invention relates to method and apparatus for depositing thin films for use in integrated circuits by forming a mist of a liquid, and depositing the mist or a vapor formed from the mist on an integrated circuit substrate, and more particularly to such a fabrication process which increases both the step coverage and deposition rate of such a process.
2. Statement of the Problem
U.S. Pat. No. 5,456,945 issued Oct. 10, 1995 describes a method of misted deposition that has proven to provide thin films of complex materials that are of the high quality necessary for integrated circuit electronic devices. The misted deposition process also achieves deposition rates that are significantly higher then the deposition rates in other methods of depositing complex materials, such as chemical vapor deposition. One reason why the method provides high quality films is that it is a low energy process, therefore the complex organic solvents and chemical compounds that are used in the process are not carbonized or otherwise destroyed in the process. However, over extreme topological features, the misted deposition process of forming the film does not provide step coverage as good as the best alternative integrated circuit fabrication process, chemical vapor deposition. Attempts have been made to improve the step coverage by using conventional methods of adding energy used in chemical vapor deposition processes, such as heating the substrate sufficiently to significantly increase the yield. These attempts have lead to films that are carbonized, fractured and of a generally low quality that is not suitable for the fabrication of integrated circuit electronic devices. The more complex the compounds one is attempting to form, the more serious the problems. Since integrated circuit materials are tending to become more complex, and liquid source deposition processes are turning out to be the most reliable for forming thin films of very high quality, it would be highly desirable to have a liquid source deposition process that retained the high quality and high deposition rates of the lower energy misted deposition process, but at the same time was capable of the excellent step coverage available in the CVD process.
Electric fields have also been used to assist in deposition of mists. However, mists used in making electrical components for integrated materials consist of metal-organic compounds, such as alkoxides and carboxylates carried by inert gases. The gases must be inert, since otherwise they can combine with the reactive metal-organic compounds and alter the deposition process. However, both the metal-organic compounds and the inert gases do not ionize well, and thus it is difficult or impossible to use the electric field for anything more than mild poling of the mists.